An ink jet recording apparatus ejects ink droplets while reciprocating a recording head for ejecting ink laterally in a state of having a short distance from a recording medium, thereby forming on the recording medium characters or an image in accordance with image data, to thus attain recording. By means of changing the color of ink to be ejected, color printing is enabled; and by means of employing inks of three colors of yellow, magenta, and cyan, full-color recording can also be readily attained. As compared with recording in black on the basis of color mixing of yellow, magenta and cyan inks, recording in black with use of a black ink is superior in terms of reduction of recording time, as well as in terms of the density of a recorded color. Therefore, four colors including the black ink are more often employed for full-color recording.
Means for miniaturization of a color ink jet recording apparatus which performs recording of a color image by ejecting inks of different colors through predetermined nozzles includes employment of a “multi-color-integrated recording head”. The multi-color-integrated recording head ejects inks of different colors from a single recording head. The multi-color-integrated recording head performs recording while grouping nozzles for the respective colors. When the nozzle groups are provided respectively for yellow, magenta, cyan, and black, full-color recording can be attained by use of the single recording head.
An ink jet recording apparatus ejects liquid ink. Accordingly, when moisture and other volatile constituents evaporate from the liquid ink, the viscosity of the ink increases. (Hereinafter, increase in viscosity caused by evaporation of moisture and other volatile constituents is referred to as “thickening”.) The thus-thickened ink causes nozzle clogging, thereby causing faulty ejection of ink. In ink jet recording of recent years, an amount of an ink droplet ejected for forming a record is of a submicroscopic size of several pL so as to achieve high-definition recording. Hence, nozzles through which inks are ejected are reduced in diameter, and energy required for ink ejection is also reduced. Since the nozzles are small in diameter, and are also small in terms of energy for ejecting ink, influences exerted on ink ejection by nozzle clogging are significant. In addition, in some cases, bubbles are trapped within the nozzles or ink supply paths, thereby rendering the condition inappropriate for ejection. Furthermore, paper, which makes up the majority of recording media for ink jet printing, produces a large amount of paper dust through a sheet feeding operation associated with recording. In some cases, the thus-produced paper dust, ambient dust, and a trace amount of small ink droplets which are produced along with ejection of ink droplets adhere to a face where the nozzles are formed (hereinafter called as a “nozzle face”) of a recording head through which inks are ejected. When foreign substances constituted of ink, paper dust, dust, and the like adhere to the nozzles and to the vicinity thereof, normal ejection of ink is inhibited.
Recovery means must be provided so as to prevent or resolve faulty ejection resulting from thickening of ink, bubble entrapment, and adhesion of foreign substances onto the nozzle face. In many cases, suction means and wipe-cleaning means are employed in combination as the recovery means. The suction means attains recovery by means of pressing a cap, which is provided with an air-communication port having a valve for establishing communication with the air, against the nozzle face, thereby forcibly sucking ink, to thus discharge ink, bubbles, foreign substances, and the like, clogged in the nozzles to the outside of the nozzles. The wipe-cleaning means wipes and cleans the nozzle face through a wiping operation of bringing a blade-like wiping member (hereinafter called a “wiper”) into close contact with the nozzle face of the recording head, and moving the wiper and the nozzle face in relation to each other. The ink adhering to the nozzle face as a result of the suction operation is removed from the nozzle face by the wipe-cleaning means. Hereinafter, a recovery operation making use of the recovery means is called “cleaning.”
When ink has been filled in a recording head prior to use of an ink jet recording apparatus, ink may be leaked during the course of distribution and storage. Therefore, ink is not filled in a recording head before distribution and storage. Upon first use, ink is sucked from an ink-retaining mechanism to the ink supply path and to the recording head, to thus be filled, in an initial filling operation. In this case, the ink suction means is also used as filling means. Furthermore, the wiping and cleaning operations are also performed so as to make the condition conducive to favorable ejection.
In actual recovery procedures, the cap is brought into close contact with the nozzle face so as to cover the nozzles of the recording head. Thereafter, ink is sucked by means of building up negative pressure within the cap by use of a suction device. As a result of this suction, ink is accumulated within the cap. Subsequently, the space within the cap is brought into communication with the air, and suction is performed again by use of the suction device, thereby discharging the ink within the cap. When the ink within the cap is successfully removed, the cap is removed. Next, the wiper is placed on the head to thus perform wiping, thereby removing unnecessary ink adhering to the vicinity of the nozzles. Subsequently, the cap is brought into close contact with the nozzle face again, and pre-ejection (flushing) of ejecting ink out of all the nozzles is performed, thereby forming ink meniscuses. After micro-bubbles and color-mixed ink in the nozzles are discharged, the cap is removed from the nozzle face. Cleaning is selectively implemented for a variety of causes (such as elapse of a given amount of time from a previous cleaning operation, or forcible cleaning which is performed upon occurrence of faulty ejection). Therefore, the amount of ink to be sucked, the number of times of wiping, and the number of flushing operations to be performed are not uniform. However, since flushing after wiping is performed for bringing the nozzles into the condition conducive to favorable ejection, the flushing is performed under substantially identical conditions irrespective of a variety of cleaning modes.
However, cleaning of a multi-color-integrated recording head involves a problem, which arises irregularly during ink suction, that ink sucked via a nozzle through a suction operation intrudes into another nozzle for another color. This problem is caused by uncontrollable causes, such as an irregular flow of ink within a cap, or the like. When ink of a different color intrudes into the nozzle, the colors of inks are mixed. When the color-mixed ink is ejected out of the nozzle, obtainment of desired recording colors on a recording medium fails. To this end, a color ink jet recording apparatus must be provided with a countermeasure for preventing color mixing on a nozzle face. In addition, the number of flushing operations for ejecting the color-mixed ink must be set in accordance with an extent of color mixing.
When ink easily wets the nozzle face in ink jet recording, the ink is spread on the nozzle face, which results in non-ejection of ink droplets. Alternatively, even when ink droplets are ejected, the ink droplets vary in size, velocity, or direction of ejection by a significant extent, thereby failing to obtain stable ejection. To this end, attempts have been made to reduce the wettability of the nozzle face against the ink, to thereby obtain stable ejection. As materials for forming an ink jet head, there have been employed silicon, glass, metals, resins, and the like, which have the property of being readily wet with ink. Hence, a method of forming a water-repellent film on the nozzle face has been proposed as a method for reducing wettability. (Patent Document 1)
As a method for resolving nozzle clogging, there has been proposed a method for cleaning a recording head, which is characterized in that both a contact angle θ1 between ink and an inner surface of a cap, and a contact angle θ2 between a nozzle face and the ink are set to 90° or smaller, where θ2≦θ1. More specifically, according to the cleaning method, clogging is recovered as follows. Both the inner surface of the cap, and the nozzle face are made to be readily wet with ink. When ink is discharged to the cap through the nozzles by a cleaning operation, the ink spreads on the cap and the nozzle face, and covers the clogged nozzles. Hence, the clog is dissolved by the ink. (Patent Document 2)
As a method for preventing color mixing of inks in nozzles which may be otherwise caused by cleaning, there has been proposed an ink jet recording apparatus. The apparatus is characterized in that its multi-color-integrated recording head has a structure, within a cap for use in ink suction, for causing inks of respective colors to flow more readily in a direction crossing a direction along which the nozzles are aligned than in the direction along which the nozzles are aligned. (Patent Document 3)
[Patent Document 1] JP-A-4-294145
[Patent Document 2] JP-A-7-290724
[Patent Document 3] JP-A-7-117242
According to the method of spreading ink on the nozzle face, thereby dissolving nozzle clogs, to thus recover the clogged nozzles, ink having been sucked into the cap during cleaning readily wets both the cap and the nozzle face. Hence, the ink on the nozzle face is likely to be uneven. Furthermore, the ink becomes further uneven as a result of wiping and cleaning during a wiping operation, which can result in unstable ejection of the ink. In order to stabilize ink ejection, the nozzle face must be wetted uniformly with ink by means of strictly adjusting a suction force for ink, the number of times and strength of the wiping operation, and the like. As a result, a period of time for cleaning becomes inevitably long, and the cleaning operation is inevitably complicated. In addition, since a load applied on a wiper during the wiping operation must be increased, durability of an ink-repellent film on the nozzle face is decreased. Furthermore, in the case where cleaning for inks of a plurality of colors is implemented, color mixing of inks occurs at the nozzles. Consequently, an amount of ink required for flushing for resolving the color mixing is increased.
A method of forming grooves in an absorptive member within the cap, a method of forming the cap from a multilayered sponge-like member, and the like, have been proposed as means for providing the structure for causing the ink to flow more readily in the direction crossing the direction along which the nozzles are aligned than in the direction along which the nozzles are aligned. When the clearances between different colors are reduced, disposition of the structure, which is to be disposed between different ink colors, for causing ink to readily, accurately flow between nozzles of different colors encounters difficulty, thereby inhibiting miniaturization of the head. Furthermore, since microprocessing must be applied on the absorptive member within the cap, cost is increased.